Update README to add usage output

README.md

@@ -24,16 +24,41 @@ We use [glide][1] for managing vendored dependencies.
 
 Certigo can read certificates/keystores in various formats and dump them to stdout.
 
-Currently supported formats are DER, PEM, JCEKS and PKCS12. It's a one-stop shop for debugging/analyzing certs.
+Currently supported formats are DER, PEM, JCEKS/JKS and PKCS12. Certigo will display information in a human-readable way, and print warnings for common mistakes (such as small key sizes or weak signatures/hash functions). Certigo can also convert any input to a series of PEM blocks, which is useful if you want to e.g. dump the contents of PKCS12/JCEKS keystores into something more useful.
 
-For example (from stdin):
+```
+usage: certigo [<flags>] <command> [<args> ...]
+
+A command line certificate examination utility.
+
+Flags:
+  --help     Show context-sensitive help (also try --help-long and --help-man).
+  --version  Show application version.
+
+Commands:
+  help [<command>...]
+    Show help.
+
+  dump [<flags>] [<file>...]
+    Display information about a certificate.
+
+  connect [<flags>] [<server:port>]
+    Connect to a server and print its certificate.
+
+  pem [<flags>] [<file>...]
+    Convert input to PEM-formatted blocks.
+```
+
+### Examples
+
+Display information about a certificate (from stdin):
 
 <img src="https://cdn.rawgit.com/square/certigo/master/examples/example_1_245953.svg" width="100%" height="100%">
 
-Or from a file:
+Display information about a certificate (from a file):
 
 <img src="https://cdn.rawgit.com/square/certigo/master/examples/example_2_d848d5.svg" width="100%" height="100%">
 
-You can dump a cert chain from a TLS server. Unlike `openssl x509 -text`, certigo will dump the entire chain, not just the first certificate:
+Display information about a certificate from a remote server:
 
 <img src="https://cdn.rawgit.com/square/certigo/master/examples/example_3_ffafad.svg" width="100%" height="100%">

examples/example_1_245953.svg

@@ -6,7 +6,7 @@
      viewBox="0 0 60 51.4">
      <rect x="0" y="0" width="100%" height="100%" fill="#f7f7f7" stroke-width="2" />
      <text font-family="monospace" font-size="1">
-       <tspan x="0.5" dy="1.2">&#36; cat certs/cert.pem | ./certigo dump</tspan>
+       <tspan x="0.5" dy="1.2">&#36; certigo dump &#60; cert.pem</tspan>
        <tspan x="0.5" dy="1.2">** CERTIFICATE 1 **</tspan>
        <tspan x="0.5" dy="1.2">Serial: 11578389349061131131</tspan>
        <tspan x="0.5" dy="1.2">Not Before: <tspan fill="green">2016-05-27 21:15:31 +0000 UTC</tspan></tspan>

examples/example_2_d848d5.svg

@@ -6,7 +6,7 @@
      viewBox="0 0 60 55">
      <rect x="0" y="0" width="100%" height="100%" fill="#f7f7f7" stroke-width="2"/>
      <text font-family="monospace" font-size="1">
-       <tspan x="0.5" dy="1.2">&#36; ./certigo dump certs/cert.jks</tspan>
+       <tspan x="0.5" dy="1.2">&#36; certigo dump keystore.jceks</tspan>
        <tspan x="0.5" dy="1.2">Enter password:</tspan>
        <tspan x="0.5" dy="1.2">** CERTIFICATE 1 **</tspan>
        <tspan x="0.5" dy="1.2">Alias: second-key</tspan>

examples/example_3_ffafad.svg

@@ -9,7 +9,7 @@
        <rect x="0" y="0" width="99%" height="100%"/>
      </clipPath>
      <text font-family="monospace" font-size="1" clip-path="url(#rect)">
-       <tspan x="0.5" dy="1.2">&#36; ./certigo connect squareup.com:443</tspan>
+       <tspan x="0.5" dy="1.2">&#36; certigo connect squareup.com:443</tspan>
        <tspan x="0.5" dy="1.2">** CERTIFICATE 1 **</tspan>
        <tspan x="0.5" dy="1.2">Serial: 1413474646</tspan>
        <tspan x="0.5" dy="1.2">Not Before: <tspan fill="green">2014-12-22 20:28:37 +0000 UTC</tspan></tspan>