gist: add two examples (#1453)

pages/common/gist.md

@@ -2,6 +2,10 @@
 
 > Upload code to https://gist.github.com.
 
+- Login in gist on this computer:
+
+`gist --login`
+
 - Create a gist from any number of text files:
 
 `gist {{file.txt}} {{file2.txt}}`
@@ -18,6 +22,10 @@
 
 `gist -l`
 
+- List all gists for the currently logged in user:
+
+`gist -l {{user_name}}`
+
 - Use the id from the gist URL to modify or include a file:
 
 `gist -u {{GIST_ID}} {{file.txt}}`